In making, for example, a tank it is known for example from copending application Ser. Nos. 11/065,135 to wind a strand, normally a filament or tape impregnated with a curable synthetic resin, onto a mandrel. The shell thus formed takes on shape whose inner surface is a body of revolution that corresponds exactly to the cylindrical or frustoconical outer surface of the mandrel. The resin is then allowed to cure into a hardened state and then the mandrel and shell are separated by relative displacement parallel to the axis of the mandrel.
Various embodiments of mandrel-extraction apparatuses are well known in practice, but all have disadvantages. With these known apparatuses, special tool parts are required for mandrels of various size or for mandrels of different diameters. This factor entails significant tool costs and retooling costs, as well as disadvantageously long retooling times. Relative high forces are required to extract the mandrel from the shell. In addition, negative forces or disturbances are often produced in the known extraction apparatuses when the mandrel is extracted which result in degradation of the quality of the shell, even including destruction of the shell. The known extraction apparatuses are thus in need of improvement.